Method of beneficiating mica



- muscovite 3,016,139 Patented Jan. 9, 1962 3,016,139 METHOD OF BENEFICIATING MICA Howard W. Adam, Gouverneur, N.Y., assign'or to International Minerals & Chemical Corporation, a corporation of New York No Drawing. Filed Sept. 29, 1959, Ser. No. 843,077

6 Claims. (Cl. 209-8) is considered the most valuable form. Muscovite is seldom found in pure form. Scrap mica from silt bed and waste deposits is usually comprised of mixtures of with biotite [K(Mg Fe) AlSi O (OH) Quite frequently waste deposit mica mixtures, and particularly mica mixtures found in silt deposits are ironstained. Such iron staining complicates seriously the problem of separating the muscovite from the biotite present in such mixtures.

It is a primary object of this invention to provide a method of separately recovering muscovite and biotite from trash or scrap mica.

It is an additional primary object of the invention to provide a method for the separation of iron-stained muscovite from iron-stained biotite mica.

It is a more specific object of the invention to provide a method for recovering muscovite from a mixture of iron-stained muscovite and iron-stained biotite present in silt mica deposits.

It is another object of this invention to provide a method of recovering relatively pure mica from silt 'deposits.

It is still another object of this invention to provide a method of removing impurities from silt deposit mica.

These and other objects of the invention will be apparent to those skilled in the art from the following description.

In accordance with this invention, it has been discovered that mixtures of iron-stained muscovite and biotite can effectively be separated by heating to a temperature of from about 300 F. to about 1800 F. under reducing conditions selectively to increase the susceptibility of the biotite to magnetic attraction, and thereafter subjecting the said mixture to magnetic separation to produce a predominantly muscovite concentrate and a predominantly biotite tail.

In siltatrash-mica mixtures, such as found at the Davy Crockett Dam in Tennessee, the biotite content is highest in fractions having the smaller particle size, for example, 2%3% biotite in the +20 mesh fraction and 30%40% biotite in the 60 mesh material. This fact adds measurably to the cleanness of the separation effected in accordance with the process of the invention. Moreover, silt mica deposits contain organic matter which effectively supplies an appropriate reducing atmosphere when the silt deposit is heated. Accordingly, as applied to silt deposit micas, the invention contemplates classifying said silt to separate a fraction thereof having a particle size of from about 4 to about 100 mesh, heating said fraction to a temperature of from about 300 F. to about 1800 F. to oxidize said organic matter and establish mild reducing conditions in said heated fraction, said reducing conditions being effective to selectively increase the susceptibility of said biotite to magnetic attraction and thereafter subjecting the resulting, substantially organic matter-free mixture to magnetic separation to pro-- duce a predominantly muscovite concentrate and a predominantly biotite tail.

-More specifically, in carrying out the process as applied to silt deposit mica, the silt deposit is dredged out and washed into flumes. Classifiers and washers remove coarse material such as pebbles, sand, and the like. The water slurry from the washers contains practically all of the mica, some fine sand and so-called trash or organic material. Additional sand removal is attained by screening operations as by means of rotary screens and water used to Wash the mica fraction substantially free of slimes.

The deslimed mica fraction, comprising a mixture of iron-stained muscovite and iron-stained biotite micas, preferably after sand removal although such is not essential to the invention, is heat treated at temperatures in the range between about 400 F. and about 1800 F. under conditions to control the oxidizing atmosphere. Because of the presence of appreciable quantities of organic matter, varying from about 3% to about 40% by weight, the burning operation is controlled to develop mild reducing conditions Within the heated medium and selectively alter theiron present on the biotite. The heat treatment under mild reducing conditions in a manner well known to the art, i.e., little free oxygen, renders the biotite more responsive magnetically than the muscovite. Preferably, the heat treatment is carried out at temperatures in the range between about 300 F and about 1800 F. If insufiicient trash is present to effect a good burning, carbonaceous material such as vegetable or petroleum coke may be added to the mica fraction. An effective burning is accomplished when organic material is present in amounts constituting about 10% to about 20% by weight of the fraction to be burned. Appropriate reducing conditions can be maintained by controlling the oxygen content of the combustion gases to less than about 1% by volume and preferablylcs's than about 0.5% by volume.

Heat treatment operations may be carried out in suitable equipment such as rotary kilns, hearth furnaces, and the like.

Material is heat treated for a period of about 10 to 30 minutes, depending upon the temperature level. About a 10 minute holding time is required for complete cornbustion of trash at temperatures in excess of about 700 F.

The heat treated material consists mainly of muscovite, biotite, ash and cinders of coal or wood.

The biotite, as a result of the mild reducing conditions, is selectively rendered more magnetic than the muscovite.

Cooled heat-treated material is magnetically separated in a dry condition. Preferably, the separation is made on a magnetic roll separator, but other magnetic separators such as gravity flow, horizontal belt and shaking tray separators may be used. More than one pass through the magnetic field, With or without differing magnetic intensity, may be employed.

In the following specific example, the magnetic separating machine employed contained a magnet having the space between magnetic poles variable between about 1 inch and about A inch. It is obvious, of course, that magnets and magnetic fields of various sizes, strengths and spacing between the magnetic poles of various distances outside the figures stated may be employed with the proper adjustments being made for the particular ore particles being processed. Although direct current magnets were employed, alternating magnets may also be used, if desired.

The following example is given by way of illustration and without any intention that the invention be limited thereto.

Example I Silt deposit at the Tennessee Valley Authority Davy Crockett Dam, Tennessee, was dredged up and washed into a flume. From the flume, the solids passed through a trommel screen to remove rock and pebble material and then to Washers where sand was removed. The material recovered from the washers consisted of fine sand, micaceous material and organic trash having a particle size in the range of about 4 mesh to about +100 mesh standard screen size.

This 4/+100 mesh fraction contained 18% sand, 62% of a mixture of iron-stained muscovite and ironstained biotite mica, and 20% organic material. This fraction was fed at the rate of 1000 pounds per hour through a rotary kiln. Solids were raised to a temperature of about 700 F. and were treated at that temperature for about minutes. Combustion gases leaving the kiln had an average oxygen content of less than about 0.5%.

Heat treated solids from the kiln were cooled in air to a temperature of about 100 F. and passed through a Carpco magnetic roll separator.

Results were as follows:

Pounds of muscovite per 100 pounds silt: 4.86

Pounds of biotite per 100 pounds silt: 1.14

Purity of muscovite: 89% muscovite, 7% biotite, 3%

sand

Purity of biotite: 49.3% biotite, 1% cinders This application is a continuation-in-part of Adam application Serial No. 559,123 filed January 16, 1956.

Having thus fully described my invention, what I claim is:

l. The process which comprises heating a mixture of iron-stained muscovite and iron-stained biotite mica at a temperature in the range of from about 300 F. to about 1800 F. under reducing conditions and thereafter subjecting the mixture to magnetic separation to produce a predominantly muscovite concentrate and a predominantly biotite tail.

2. The process which comprises forming a mixture containing iron-stained muscovite, iron-stained biotite, and from about 10% to about 20% by weight of organic material, heating said mixture to a temperature within the range of about 300 F. to about 1800 F. to eitect combustion of said organic material under reducing conditions to selectively increase the susceptibility of the biotite to magnetic attraction and thereafter subjecting said mixture to magnetic separation to produce a predominantly muscovite concentrate and a predominantly biotite tail.

3. The process of claim 2 wherein the oxygen content of the combustion gases formedby the combustion of said organic material is maintained at a concentration of less than about 1% by volume.

4. The process of claim 2 wherein the oxygen content of the combustion gases formed by the combustion of said organic material is maintained at a concentration of less than about 0.5% by volume.

5. The process for recovery of muscovite from silt containing muscovite, biotite, sand and organic matter which comprises classifying said silt to separate a fraction thereof having a particle size of from about 4 to about mesh, heating said fraction to a temperature ture of from about 300 F. to about 1800 F. to oxidize said organic matter and establish mild reducing conditions in said heated fraction, said reducing conditions being effective to selectively increase the susceptibility of said biotite to magnetic attraction and thereafter subjecting the resulting, substantially organic matter-free mixture to magnetic separation to produce a predominantly muscovite concentrate and a predominantly biotite tail.

6. The process of claim 5 wherein said organic material constitutes from about 3% to about 40% by Weight of said silt.

References, Cited in the file of this patent UNITED STATES PATENTS 1,999,825 Saklatwalla et a1. Apr. 30, 1935 2,132,404 Dean et a1. Oct. 11, 1938 2,240,718 Schiffman et a1. May 6, 1941 2,302,981 Stern Nov. 24, 1942 2,765,074 Diamond Oct. 2, 1956 

1. THE PROCESS WHICH COMPRISES HEATING A MIXTURE OF IRON-STAINED MUSCOVITE AND IRON-STANTED BIOTITE MICA AT A TEMPERATURE IN THE RANGE OF FROM ABOUT 300* F. TO ABOUT 1800* F. UNDER REDUCING CONDITIONS AND THEREAFTER SUBJECTING THE MIXTURE TO MAGNETIC SEPARATION TO PRODUCE A PREDOMINAMTLY MUSCOVITY CONCENTRATE AND A PREDOMINANTLY BIOTITE TAIL. 